1. Field of the Invention
The present invention relates to an optical disc device that uses an optical beam emitted from a light source such as a laser to reproduce information recorded optically on an information carrier. In particular, the present invention relates to a track jumping control for conducting a shift from an arbitrary track to another track on an information carrier in which a spiral information track formed as an uneven guide groove is divided in a radial direction and has an address part where position information is recorded in advance.
2. Description of the Related Art
In a conventional optical disc device, a tracking control is performed by shifting a converging lens in the radial direction of an information carrier using a tracking actuator. This tracking actuator is constructed of a fixed part and a movable part that is mounted on a converging lens, and the movable part and the fixed part are coupled together with an elastic body such as four pieces of wires (wire rod), rubber or the like. Then, when an electric current is supplied to a coil in the movable part, an electromagnetic force is generated between the coil and a permanent magnet in the fixed part, and this electromagnetic force allows the converging lens to move in the radial direction of the information carrier, that is, in the direction perpendicular to the track.
A search for a desired information track is carried out by deactivating the tracking control, shifting an optical head including the tracking actuator as a whole in the radial direction of the information carrier, and counting tracks which were crossed by a convergent point of an optical beam on the information carrier. Here, when the number of tracks to the desired information track is several tracks, in order to reach the desired information track surely and stably, an accelerating/decelerating pulse is applied to the tracking actuator while retaining the tracking control in the activated state, and a track jumping of moving to the neighboring track is performed repeatedly.
In recent years, along with the improvement of high-density optical disc technology, a recordable optical disc (DVD-RAM) has come into being. This recordable DVD-RAM disc includes an address part and a recordable data part. Furthermore, this DVD-RAM disc is divided into a plurality of zones in the radial direction, and the data part is formed as a convex groove (referred to as a groove track) and a guide groove of a region interposed between adjacent grooves (referred to as a land track). FIGS. 12A, 12B and 12C are schematic diagrams showing the structure of such an optical disc. FIG. 12A is a partial cutaway perspective view showing the whole structure of an optical disc; FIG. 12B is a perspective view showing an enlarged cross-section of an optical disc 101 cut in the radial direction; and FIG. 12C is a schematic diagram showing the relative position between an address part and a data part. As shown in FIG. 12C, the data part is formed as one spiral structure with grooves and a land, and the address part is formed between the grooves/lands. A convergent point of an optical beam on the optical disc 101 is larger than a track width, and when the convergent point of the optical beam scans the grooves or the lands, address information stored in the address part between these tracks also can be read out.
In the following, a conventional track jumping method for this DVD-RAM disc will be explained in detail with reference to the drawings. FIG. 11 is a block diagram showing a simple configuration of an optical disc device for performing a conventional track jumping method. A conventional optical disc device is provided with a disc motor 102 for rotating the optical disc 101 at a predetermined number of revolutions, an optical head 103 (including a light source such as a semiconductor laser, a coupling lens, a deflected beam splitter, a deflection plate, a converging lens, a condensing lens, a split mirror, a photodetector and so on, which are not shown in the drawing) for reproduction of information from the optical disc 101, and a traverse motor (not shown in the drawing) for shifting the optical head 103 as a whole in a direction perpendicular to the direction of tracks of the optical disc 101.
An optical beam spot formed by the optical head 103 is emitted to the optical disc 101 that is rotated by the disc motor 102. A light reflected from the optical disc 101 passes through a converging lens, a deflection plate, a deflected beam splitter, and a condensing lens and is split into two-way optical beams by a split mirror. One of the split optical beams is input to a focus control device (not shown in the drawing) via a split-structure photodetector to generate a positional displacement signal (a focus error signal, hereinafter abbreviated as a xe2x80x9cFE signalxe2x80x9d) between the convergent point of the optical beam and the optical disc 101 based on a difference in the output of the photodetector, and performs a focus control based on this FE signal so that the convergent point is positioned on the optical disc 101. The configuration and the operation of the focus control device is not directly related to the explanation of the track jumping method, so that the explanation thereof is omitted.
On the other hand, the other optical beam that was split by the split mirror is input to a tracking control device via the split-structure photodetector. The tracking control device includes a tracking error signal generator 104, a digital signal processor (DSP) 1101, a tracking driving circuit 110 and a tracking actuator (not shown in the drawing). The tracking error signal generator 104 generates a signal indicating a displacement of the convergent point of the optical beam on the optical disc 101 with the track, that is, a tracking displacement signal (tracking error signal, hereinafter abbreviated as a xe2x80x9cTE signalxe2x80x9d) for controlling the convergent point of the optical beam on the optical disc 101 in order to scan the surface of the track based on a difference in the output of the split-structure photodetector, and this TE signal is input to the DSP 1101. A method for detecting this TE signal is called xe2x80x9ca push-pull methodxe2x80x9d.
A switch 108 is provided in the DSP 1101. The switch 108 is set at a position shown by the solid line when a tracking control is switched on, whereas the switch 108 is set at a position shown by the dotted line when a track jumping to a neighboring track is performed. Therefore, the switch 108 is operated to open and close the loop of a tracking control system and also to switch a driving signal to be supplied to the tracking actuator for performing a tracking control and for performing a track jumping.
First, a tracking control will be explained. The TE signal input to the DSP 1101 is converted from an analog signal to a digital signal by an AD converter 105 and input to a compensating filter 106, which is a digital filter including an adder, a multiplier and a delay element. The compensating filter 106 serves to compensate a phase or the like of the tracking control system. The TE signal whose phase was compensated by the compensating filter 106 is input to the switch 108 via a gain switching circuit 107 that switches a loop gain of the tracking control system. The switch 108 is set at a position shown by the solid line for performing a tracking control, so that the TE signal that passed through the switch 108 is converted from a digital signal to an analog signal by a DA converter 109 and input to the tracking driving circuit 110.
The tracking driving circuit 110 drives the tracking actuator by appropriately performing a current amplification and a level conversion of an output signal from the DSP 1101. Thus, the tracking actuator is driven such that the convergent point of the optical beam on the optical disc 101 scans a predetermined surface of the track, thereby achieving a tracking control. Here, in the case of a DVD-RAM disc, a tracking control is achieved by switching the polarity of the TE signal in the AD converter 105 between a time a tracking control is switched on in a groove of a convex portion and a time a tracking control is switched on in a land of a concave portion.
In accordance therewith, a transfer control is performed, which is to drive the traverse motor such that, when the convergent point of the optical beam on the optical disc 101 scans the surface of the track, the convergent point of the optical beam is matched with the center of the converging lens, that is, an optical axis of the optical beam focused and emitted to the optical disc 101 is matched with an optical axis of the converging lens. However, the explanation thereof is omitted.
Next, a track jumping in a DVD-RAM disc will be explained with reference to the waveform charts of FIG. 13 in addition to the block diagram of FIG. 11. FIGS. 13A, 13B and 13C are waveform charts of a TE signal, an address gate signal and a tracking driving signal at the time a track jumping (one line jumping) is performed from a land to a land in an inner circumferential direction. When a track jumping is performed in an outer circumferential direction, only the polarity of the TE signal and that of the tracking driving signal are reversed, so that the waveform charts and explanations thereof are omitted. Furthermore, when a track jumping is performed from a groove to a groove in an inner circumferential direction, only the polarity of the TE signal is reversed, so that the waveform charts and explanations thereof also are omitted.
As is clear from the block diagram of FIG. 11, when a track jumping is performed, the tracking actuator is driven by a sum signal of a signal that passed through the gain switching circuit 107 and a low-pass filter 112, and an accelerating/decelerating pulse signal generated in an accelerating/decelerating pulse generator 113. Here, a cutoff frequency of the low-pass filter 112 is set to be low to an extent to which an eccentric component of the optical disc 101 passes sufficiently, and a low-frequency component (eccentric component) of the TE signal is added to the accelerating/decelerating pulse signal for driving the tracking actuator, so that the tracking jumping becomes less unstable due to eccentricity of the optical disc 101.
The address part of a DVD-RAM disc is located in an offtrack position between the grooves/lands, as shown in FIG. 12C. In addition, due to the configuration in which one address part consists of an address part 1 that is located in an offtrack position in the inner circumferential direction and an address part 2 that is located in an offtrack position in the outer circumferential direction of the disc, when a convergent point of an optical beam passes through the address part, a sine wave shaped waveform occurs in the TE signal, as shown in FIG. 13A. An address part detection circuit 115 generates a signal that becomes high in the address part (address gate signal), as shown in FIG. 13B. The accelerating/decelerating pulse generator 113 detects a trailing edge of the address gate signal, then waits for a predetermined time (Twait), sets the switch 108 to a position for track jumping shown by the dotted line and starts to output an accelerating pulse (predetermined peak value A1). Thus, the optical head 103 starts to move toward the inner circumferential direction of the optical disc 101, and along with this movement, a sine wave TE signal occurs. After the accelerating pulse is output for a predetermined time (T1), it is in a wait state until a zero-cross-point of the TE signal is detected. Here, the detection of the zero-cross-point is performed by detecting an intersection point of the TE signal that passed through the gain switching circuit 107 with an output signal of the low-pass filter 112. Next, the accelerating/decelerating pulse generator 113 starts to output a decelerating pulse (predetermined peak value A2), and the decelerating pulse is output for a predetermined time (T2). Thereafter, by setting the switch 108 to a position for a tracking control shown by the solid line, the track jumping from a land to a land in the inner circumferential direction is completed. Then, a tracking control is resumed.
Here, a method employed to carry out a rotational control of the disc motor 102 at the time a DVD-RAM disc is reproduced is a method in which a number of revolutions, which is the same in the same zone, is reduced gradually from the inner circumference to the outer circumference (ZCLV method). According to this method, a time-interval from an address part to the next address part always becomes a constant time (about 1.5 ms for a standard-speed reproduction).
According to the configuration of the conventional optical disc described above, when a track jumping is performed, the optical disc device detects the trailing edge of an address gate signal, then waits for a predetermined time, and starts to output an accelerating pulse. However, when the time interval between an address part and the next address part becomes too short due to a high-speed reproduction or immediately after accessing an outer circumference from an inner circumference in a device with a disc motor having a slow response, an output of a decelerating pulse for a track jumping is completed immediately before the next address part, so that a tracking control may be resumed. At this time, a diffracted light from the address part causes a disturbance in the tracking control system, and due to the influence thereof, the tracking control becomes unlocked. Therefore, there was a problem of failing to carry out a track jumping.
It is an object of the present invention to solve the above-mentioned conventional problems by providing an optical disc device exhibiting stable track jumping performance, in which a reproduction speed is detected at a time a track jumping starts, and when the reproduction speed is faster than a predetermined reproduction speed, a start position of jumping is switched in order to match the application timing of an accelerating pulse or a decelerating pulse for a track jumping with the transit timing in an address part.
In order to achieve the above-mentioned object, an optical disc device according to the present invention includes shifting means for shifting a convergent point of an optical beam focused on an information carrier in which an information track is divided in a radial direction and has an address part in a direction crossing the track on the information carrier, track displacement detection means for generating a signal corresponding to a relative position between the convergent point of the optical beam and the track, tracking control means for driving the shifting means according to an output signal from the track displacement detection means and controlling the convergent point of the optical beam to scan a surface of the track, track jumping means for shifting the convergent point of the optical beam from an arbitrary track to another track on the information carrier, jumping starting means for operating the track jumping means and starting an application of an accelerating signal, and reproduction speed measuring means for measuring a speed at which information on the information carrier is read out, wherein the jumping starting means operates the track jumping means based on a position of the address part on the information carrier and a measuring result from the reproduction speed measuring means.
In a first configuration of an optical disc device according to the present invention, it is preferable that the reproduction speed measuring means includes address part detection means for detecting an address part on the information carrier and address space measuring means for measuring a time interval between two or more consecutive address parts based on an output signal of the address part detection means, and that a reproduction speed is measured by comparing a measuring result from the address space measuring means with a predetermined time. Based on a measuring result from the reproduction speed measuring means, the jumping starting means operates the track jumping means by starting an application of an accelerating signal after the address part is detected and the predetermined time has passed thereafter.
In this case, it is preferable that the address part detection means includes binarization means for converting an output signal from the track displacement detection means or a signal for reproduction of information on the information carrier into two values at a predetermined level in order to detect the address part on the information carrier.
Furthermore, it is preferable that the optical disc device includes reproduction speed comparative means for comparing the reproduction speed measured by the reproduction speed measuring means with a predetermined reproduction speed, wherein when the measured reproduction speed is found to be faster than the predetermined reproduction speed as a result of comparison by the reproduction speed comparative means, the jumping starting means operates the track jumping means by starting an application of an accelerating signal such that an application timing of the accelerating signal or a decelerating signal is matched with a transit timing in the address part.
In this case, it is preferable that the optical disc device includes address part transit time measuring means for measuring a time at which a convergent point of an optical beam passes through the address part, wherein an application time of the accelerating signal or the decelerating signal from the track jumping means is set to be longer than a time measured by the address part transit time measuring means.
Furthermore, it is preferable that the track jumping means includes first track jumping means for shifting a convergent point of an optical beam from an arbitrary track to another neighboring track and second track jumping means for shifting a convergent point of an optical beam to another neighboring track by skipping one track therebetween, and the jumping starting means switches a time interval from the detection of the address part to the operation of the track jumping means between a time the first track jumping means is operated and a time the second track jumping means is operated.
Furthermore, it is preferable that the optical disc device includes reproduction speed comparative means for comparing the reproduction speed measured by the reproduction speed measuring means with a predetermined reproduction speed, wherein when the measured reproduction speed is found to be slower than the predetermined reproduction speed as a result of comparison by the reproduction speed comparative means, the jumping starting means operates the track jumping means in an intermediate position between consecutive address parts.
Alternatively, in a second configuration of an optical disc device according to the present invention, it is preferable that the reproduction speed measuring means includes address part detection means for detecting an address part on the information carrier and address part transit time measuring means for measuring a time at which a convergent point of an optical beam passes through the address part, and that a reproduction speed is measured by comparing a measuring result from the address part transit time measuring means with a predetermined time. Based on a measuring result from the reproduction speed measuring means, the jumping starting means operates the track jumping means by starting an application of an accelerating signal after the address part is detected and the predetermined time has passed thereafter. The above-mentioned first configuration requires a time for at least two addresses for calculation of the reproduction speed in order to measure a time from a certain address part to the next address part, whereas this second configuration can reduce the time required for calculation of the reproduction speed since a transit time in the address part itself is measured, so that a track jumping can be started earlier.
In this case, it is preferable that the address part detection means includes binarization means for converting an output signal from the track displacement detection means or a signal for reproduction of information on the information carrier into two values at a predetermined level in order to detect the address part on the information carrier.
Furthermore, it is preferable that the optical disc device includes reproduction speed comparative means for comparing the reproduction speed measured by the reproduction speed measuring means with a predetermined reproduction speed, wherein when the measured reproduction speed is found to be faster than the predetermined reproduction speed as a result of comparison by the reproduction speed comparative means, the jumping starting means operates the track jumping means by starting the application of an accelerating signal such that an application timing of an accelerating signal or a decelerating signal is matched with a transit timing in the address part.
In this case, it is preferable that the application time of the accelerating signal or the decelerating signal by the track jumping means is set to be longer than a time measured by the address part transit time measuring means.
Furthermore, it is preferable that the track jumping means includes first track jumping means for shifting a convergent point of an optical beam from an arbitrary track to another neighboring track and second track jumping means for shifting a convergent point of an optical beam to another neighboring track by skipping one track therebetween, and the jumping starting means switches a time interval from the detection of the address part to the operation of the track jumping means between a time the first track jumping means is operated and a time the second track jumping means is operated.
Furthermore, it is preferable that the optical disc device includes reproduction speed comparative means for comparing the reproduction speed measured by the reproduction speed measuring means with a predetermined reproduction speed, wherein when the measured reproduction speed is found to be slower than the predetermined reproduction speed as a result of comparison by the reproduction speed comparative means, the jumping starting means operates the track jumping means in an intermediate position between consecutive address parts.
Alternatively, in a third configuration of an optical disc device according to the present invention, it is preferable that the reproduction speed measuring means includes address part detection means for detecting an address part on the information carrier, reproduction signal detection means for generating a signal for reproduction of information on the information carrier by a reflected light or a transmission light from the information carrier, address readout means for reading out address information in the address part obtained by an output signal from the reproduction signal detection means, radial position calculation means for calculating a radial position of a convergent point of an optical beam on the information carrier based on the address information from the address readout means, and rotation number measuring means for measuring the number of revolutions of the rotating information carrier. Based on a measuring result from the reproduction speed measuring means, the jumping starting means operates the track jumping means by starting an application of an accelerating signal after the address part is detected and a predetermined time has passed thereafter.
In this case, it is preferable that the optical disc device includes reproduction speed comparative means for comparing the reproduction speed measured by the reproduction speed measuring means with a predetermined reproduction speed, wherein when the measured reproduction speed is found to be faster than the predetermined reproduction speed as a result of comparison by the reproduction speed comparative means, the jumping starting means operates the track jumping means by starting an application of an accelerating signal such that an application timing of an accelerating signal or a decelerating signal is matched with a transit timing in the address part.
Furthermore, it is preferable that the optical disc device includes address part transit time measuring means for measuring a time at which a convergent point of an optical beam passes through the address part, and an application time of the accelerating signal or the decelerating signal from the track jumping means is set to be longer than a time measured by the address part transit time measuring means.
Furthermore, it is preferable that the track jumping means includes first track jumping means for shifting a convergent point of an optical beam from an arbitrary track to another neighboring track and second track jumping means for shifting a convergent point of an optical beam to another neighboring track by skipping one track therebetween, and the jumping starting means switches a time interval from the detection of the address part to the operation of the track jumping means between a time the first track jumping means is operated and a time the second track jumping means is operated.
Furthermore, it is preferable that the optical disc device includes reproduction speed comparative means for comparing the reproduction speed measured by the reproduction speed measuring means with a predetermined reproduction speed, wherein when the measured reproduction speed is found to be slower than the predetermined reproduction speed as a result of comparison by the reproduction speed comparative means, the jumping starting means operates the track jumping means in an intermediate position between consecutive address parts.